Conventionally, there are cases where, before emitting of so-called “industrial waste gases”, such as exhaust gases of boilers in factories and smoke massively emanated from power generating plants, into the atmosphere, air purification processing is performed to remove various types of fine particulates contained in the industrial waste gases, such as mist and dust containing, for example, powders containing oil, moisture, and/or the like, which can pollutes the atmosphere. Direct emission of the industrial waste gases containing the fine particulate into the atmosphere significantly affects the global environment, so that there are cases where it is obligatory to perform collection thereof by standards of a nation or local governments. In addition, in municipal regions, air pollution resulting from, for example, automobile exhaust gases, is a serial issue, and thus even ordinary homes have and use an air cleaning apparatus. Further, in many sites, such as kitchens of restaurants, there are air cleaning apparatuses for cleaning air before emitted to the outside, for example, polluted air and smoke generated during cooking or the like.
As a dust collector that is used to collect fine particles contained in polluted air which causes air pollution and to carry out purification to clean air, there are known various types classified according to a dust collection principle. More specifically, in term of the collection principle, the apparatuses can be classified into types, such as filtration, gravitational, inertial, centrifugal, dust precipitation, and washing types. They are appropriately selected for practical use depending on, for example, the size and type of fine particulate to be collected, and/or the installation conditions of the apparatuses. In particular, of the types described above, the filtration type (using a bug filter or the like) and the dust precipitation type are excellent from the viewpoint of the dust collection capability, and thus they are widely used in various industrial fields.
The dust collection principle of electrostatic dust precipitators is such that electric charges are supplied to the fine particulate through corona discharges generated from discharge electrodes, and coulomb forces are used to electrostatically attract the charged fine particulate onto collector electrodes which are opposed electrodes, whereby the fine particulate is collected. As features, the electrostatic dust precipitator has significant advantages, such as: 1) the pressure loss is small; 2) a large amount of gases is can be processed; and 3) the collection efficiency is high. Therefore, electrostatic dust precipitators are used in such environments as factories and power generating plants which emit a large amount of polluted air.
Generally, a main construction of an electrostatic dust precipitator includes discharge electrodes each formed into a shape having a large surface curvature, such as a needle or wire material, for generating corona discharges for supplying electric charges to the fine particulate; collector electrodes, as opposed electrodes, each formed into a flat plate for collecting the charged fine particulate; a rectifier unit for rectifying the flow of gas streams in the electrostatic dust precipitator; a dust removal device (dry type) or a spray device (wet type) for separating deposited fine particulate from the collector electrodes; a hopper for collecting the separated fine particulate; and a power system and electric charge control device provided as appendages to cause corona discharges. The dust removal unit is used with a dry electrostatic dust precipitator and is used in such a manner that the collector electrodes are rapped by a hammer or the like to dislodge collected fine particulate therefrom, thereby to store the fine particulate into a collection unit, such as a hopper, provided in a lower portion. In the wet type, fine particulate collected onto the collector electrodes is washed and removed with injected cleaning solution, such as water. In a state where a large amount of the fine particulate is collected onto the collector electrodes, the coulomb force for attracting the charged fine particulate may be reduced, thereby reducing the collection efficiency. Therefore, in order to prevent the case where the dust collection cannot be performed in a stable state, the dry and wet types are used to remove the fine particulate from the collector electrodes.
In addition, in recent years, there has been deployed an apparatus of the type in which discharge electrodes and collector electrodes are housed in a cartridge so that the cartridge is replaceable. According to this type, when a large amount of the fine particulate has been deposited onto the collector electrodes to the extent of reducing the collection efficiency, the collection efficiency can be maintained constant by replacement of the cartridge. In many cases, used cartridges undergo removal of the fine particulate in, for example, dedicated facilities installed in a maker, to be reusable. Thereby, the maintenance operations of apparatuses are facilitated; and in addition, since removal facilities such as described above need not be provided, the apparatus can be downsized. Consequently, the manufacturing cost can be reduced.
However, as already described, in the case of dry and wet electrostatic dust precipitators, there is a tendency to be enlarged in size, so that installation places therefore have been often restricted to, for example, large factories and power generating plants. In the case of the cartridge type, in an environment where a large amount of polluted air is processed in a batch, whenever collection efficiency falls, the replacement of the cartridge has to be frequently done, whereby operator's labor burden, replacement costs, and the like increase, therefore potentially making the processing uneconomical. Further, there has been a demand for an electrostatic dust precipitator that has a compact shape installable in a kitchen of a restaurant or the like and that enables it to secure high collection efficiency. In view of the situations as described above, the present applicant invented an electrostatic dust precipitator having a novel configuration and already submitted a patent application therefore (Japanese Patent Application Laid-Open No. 2003-126729).
Accordingly, under these circumstances, an object of the present invention is to provide an electrostatic dust precipitator that is formed into a compact shape and hence installable even in a narrow place and that has low probability of reducing the collection capability of collecting the fine particulate and generation efficiency of corona discharges even during and after a long-time operation.